Please note that the modes "Auto Black (if no video)" and "Bidirectional Master" are different.
"Bidirectional Master" always uses a 625 carrier signal for bi-directional audio transmission between the 2 PDM1383 modules.
"Auto Black" always outputs the last connected video standard.
So e.g. if you connect and disconnect a 720p59, you will get a 720p59 output if "Auto Black" is enabled and a 625 output when working in bi-directional mode.